1. Field of the Invention
This invention concerns the improvement of a fundus camera which can take photographs by infra-red excited fluorescence.
2. Description of the Prior Art
Conventionally, a fundus camera is known which can take photographs by infra-red excited fluorescence, photographs by visible light excited fluorescence, and photographs other than those taken by fluorescence.
This fundus camera is provided with an illuminating optical system which illuminates a fundus with illuminating light, the range of illumination being determined by a field diaphragm in the illuminating optical system, and which photographs an image of the fundus within the predetermined range.
However, if a fundus disorder such as a block in a retinal blood vessel due to bleeding should occur when taking a photograph by fluorescence, the amount of fluorescent agent in the part of the fundus affected by bleeding decreases leading to a reduced fluorescence so that a good image is not obtained when a photograph is taken.
To increase the fluorescence, the amount of light emitted by the illuminating light source could be increased.
However, if the amount of light emitted by the illuminating light source is increased, although the brightness of the fluorescence in the part of the fundus affected by bleeding increases to a suitable level for the purpose of taking a photograph, the brightness of the fluorescence from other parts of the fundus becomes too intense so that a clear photographic image is not obtained.
In addition, deterioration of the image in the part of the fundus affected by bleeding could not be avoided.